The dual sphere superconducting gravimeter GWR CD029 at Frankfurt a.M. and Wettzell — first results and calibration

The first dual sphere superconducting gravimeter CD029 is operating since November 1998, at first at the test site Frankfurt A.M., further permanently at Wettzell (Bavarian Forest, Germany). The GWR dual sphere superconducting gravimeter, developed by GWR Instruments, Inc., San Diego, California, USA, enables enhanced consistencies in data and drift monitoring to achieve a high resolution and reliability for studying temporal gravity variations. The dual sphere system is equivalent to two single instruments, but the technical expenditure and the costs are considerably reduced. By differencing the signals of both systems even micro steps can be detected. The first experiences with the CD029 show, that it meets the expectations. Under regular conditions noise and drift rate are very small. No steps were observed at Wettzell down to a level of some nm s2, besides those occurred during maintenance activities. The scale factors of both systems of the C029 have been estimated by the acceleration method and by comparisons with absolute gravity measurements.